1. Field of the Disclosure
The present disclosure relates generally to control of sensors used in imaging devices such as printers and scanners, and more particularly to control of a failing or failed sensor allowing for continued operation of the imaging device.
2. Description of the Related Art
A media-full sensor is used to tell the controller in an imaging device when the output bin is full so the imaging device can pause printing or scanning This stops the imaging device from ejecting pages into the output bin that may push previous pages onto the floor. This also prevents paper jams caused by the peek-a-boo duplexer jamming paper into a stack in the output bin. In one form the media-full sensor comprises an infrared LED and a photo-transistor positioned on opposite sides of the bin that are separated by approximately 24 cm. The LED and photo-transistor are typically positioned transverse to the media path. The LED emits an infrared beam that with the media bin not full reaches the photo-transistor actuating the photo-transistor to change its state.
In Table 1, a truth table shows the digitized photo-transistor output of the media-full sensor for various fill conditions in the output bin and operational states of the LED.
TABLE 1ConditionDigitized Photo-Transistor OutputBin is emptyLow (light reaches the photo-transistor)Bin is partially fullLow (light reaches the photo-transistor)Bin is fullHigh (no light reaches the photo-transistor)LED is broken, bin isHigh (no light reaches the photo-transistor)emptyLED is broken, bin isHigh (no light reaches the photo-transistor)full
The truth table shows a problem with this sensor: a broken or failing LED looks just like a bin full condition. Thus, the imaging device will stop when the LED fails or breaks. The imaging device will refuse to operate until a service person goes onsite and fixes the sensor. A failed LED is one which emits no light or emits a light at such a low level that it is of insufficient intensity to activate the photo-transistor. It should also be stated that the photo-transistor may also fail instead of the LED but the LED is orders of magnitude more likely to fail first due to the higher currents and higher heat involved with energizing the LED to emit a light beam that will reach the photo-transistor on the opposite side of the output bin. Also field experience has soon that failure of the bin full sensor due to a failed photo-transistor is extremely rare. What is needed is a method that allows the media-full sensor to fail gracefully, i.e., a soft failure, such that a failed sensor does not stop the imaging device.